Reactive oxygen species (ROS) are chemically reactive molecules formed due to incomplete reduction of oxygen and include superoxide anions (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (HO). ROS are highly reactive due to the presence of unpaired electrons. ROS are natural byproducts of normal metabolism of oxygen in many organisms and play an important role in cell signaling and homeostasis. However, elevated levels of ROS can have detrimental results. The levels of ROS can increase dramatically when an organism is exposed to various environmental stresses such as exposure to heat, excessive light, drought, anoxia, toxins, pathogens, and the like, resulting in oxidative damage and cell death. In plants, for example, oxidative damage from excess ROS can result in reduced photosynthetic efficiency. Plants and other organisms have endogenous ROS metabolizing enzymes such as superoxide dismutase, catalase and peroxidase for preventing the buildup of ROS. However, these endogenous protective mechanisms can be insufficient when the organism experiences environmental stress conditions.